The present invention relates to hypodermic syringes, and relates more particularly to such a hypodermic syringe which has a safe needle cap that can be securely fastened to the neck of the barrel in the inverted position to stop the needle cannula inside the barrel after the use of the hypodermic syringe.
The needle cannula of a hypodermic syringe must be damaged after its use, and then properly disposed of. Various safety hypodermic syringes have been disclosed, and have appeared on the market. Exemplars are seen in Taiwan Utility Patent No. 84,837, U.S. Pat. No. 5,328,475. These hypodermic syringes permit the needle cannula to be pulled backwards to the inside of the barrel after its use. However, these hypodermic syringes cannot prevent the deformed needle cannula from projecting or escaping out of the neck of the barrel because the needle cap cannot be securely fixed to the barrel to seal the neck thereof. FIG. 1 shows the needle cap of a conventional hypodermic syringe. This structure of needle cap has a plurality of longitudinal grooves around the periphery. Because the needle cap is longitudinally grooved, it can be positively seized in the hand, then disconnected from the neck of the barrel and removed from the needle cannula. However, if the needle cap is invertedly inserted into the neck of the barrel after the needle cannula has been pulled back to the inside of the barrel, it will disconnect from the neck of the barrel easily when the barrel is shaken. Therefore, this structure of needle cap cannot seal the needle cannula of the used hypodermic syringe inside the barrel.